Drive belt

ABSTRACT

The invention relates to a drive belt, in particular suitable for a continuously variable transmission, the configuration of the drive belt being such that the tilting of the transverse elements of the drive belt in the pulley of the continuously variable transmission is largely overcome. The drive belt can be produced in a relatively simple and cheap way, offers a higher efficiency and less wear.

The invention relates to a drive belt, in particular suitable for use ina continuously variable transmission, comprising at least one endlesscarrier, and transverse elements positioned on the carrier, thetransverse elements being provided with one or more recesses for theaccommodation of the carriers, while the recesses comprise at least onebearing surface and one top surface.

Such a drive belt is known from U.S. Pat. No. 5,004,450, and is used inparticular in continuously variable transmissions. The drive belt inthat case is placed around two pulleys. The pulleys each comprise twosheaves, the distance between which is adjustable. Varying the distancebetween the sheaves of the two pulleys will move the drive belt todifferent radial positions on the pulleys, with the result that thetransmission ratio is adjustable.

It is also known from U.S. Pat. No. 4,854,919 that the geometricaldesign of the pulley/drive belt combination often causes the drive beltto run out of true between the two pulleys, so that it also runsslightly out of true into the pulleys. The transverse elements of thedrive belt are consequently received in the pulley slightly tilted in aplane at right angles to the carriers. This phenomenon is recognized inU.S. Pat. No. 5,004,450, and is overcome there by designing the contactfaces of the transverse elements in such a way that the tiltedtransverse elements automatically correct their position in the pulleysand straighten up. This works well per se, but the transverse elements,on account of their configuration and narrow tolerances, are difficultto produce and are relatively expensive. Great forces also occur, withthe result that overdimensioning of the transverse elements isnecessary.

The object of the invention is to provide a drive belt in which thetilting of the transverse elements is largely overcome, and which isalso relatively simple to produce, is guaranteed to wedge well in thepulleys, and need not be overdimensioned. For this purpose, theinvention is characterized in that in the tilted position of atransverse element in a plane at right angles to the carriers at leasttwo points can be determined, a first point which determines a contactpoint of a bearing surface with one or more carriers, and a second pointwhich determines a contact point of a top surface with one or morecarriers, in a straight position of the transverse element in the axialdirection of the drive belt the first point and the second point lyingat a distance A from each other, and also in a straight position of thetransverse element in the radial direction of the drive belt the carrierand the second point lying at a distance B from each other, in such away that the arc tangent of the quotient B/A is less than 1°.

In the drive belt according to the invention, the transverse element, onthe one hand, has sufficient play to position itself relative to thecarriers and the pulleys, while, on the other hand, a tilting of thetransverse elements is prevented in such a way that good wedging in thepulleys is ensured. The drive belt according to the invention isrelatively simple and cheap to produce.

The invention can be used in particular for drive belts which use one ortwo carriers.

Particularly in the range in which the arc tangent is greater than 0.2°and smaller than 0.8°, the effectiveness is increased, and in particularan improved efficiency of the transmission is also obtained. The arctangent is preferably approximately 0.5°.

According to a further development of the invention, one or moretransverse elements are provided with projection/recess means, in whichcase a projection of one transverse element can be accommodated withsome play in the recess of an adjacent transverse element. The play inthis case is preferably essentially in the axial direction of the drivebelt between projection and recess. This measure means that thetransverse elements can position themselves in the optimum way not onlyrelative to the pulley and the carriers, but also relative to theadjacent transverse elements.

The invention also relates to a transverse element suitable for use inthe drive belt according to the invention.

The invention will be explained with reference to a drawing. In thedrawing:

FIG. 1 shows a diagrammatic representation of a continuously variabletransmission provided with a drive belt according to the invention;

FIG. 2 shows a top view of a drive belt running out of true into thepulley;

FIG. 3a shows a drive belt in cross-section, with a transverse elementin the tilted position, for wedging in the pulley;

FIG. 3b shows a drive belt according to FIG. 3a during wedging in thepulley;

FIG. 4 shows a drive belt according to the invention in cross-section,with a transverse element in the straight position.

The continuously variable transmission i shown diagrammatically in FIG.1 comprises a pulley 3 disposed on a first shaft 2, a pulley 5 disposedon a second shaft 4, and a drive belt 6 positioned around the pulleys 3,5. The drive belt 6 comprises one or more endless carriers 7, whichcarriers themselves can consist of one or more rings combined to theform of a carrier. Transverse elements 8 are disposed on the carriers 7,which elements generally slide over the carriers 7. It is assumed herethat the way in which the continuously variable transmission 1 works isknown.

FIG. 2 shows in top view the run-in of the drive belt into the pulley 3with sheaves 9, 10. As explained in detail in U.S. Pat. No. 4,854,919,the geometrical shape of the continuously variable transmission willoften cause the drive belt 6 to run out of true into the pulley 3. Theconsequences of this running out of true can be largely overcome by themeasures according to U.S. Pat. No. 4,854,919. The running out of truedoes cause the transverse elements 8 of the drive belt 6 to come intocontact first with the sheave 10, and there is no contact yet withsheave 9. As a result, the transverse element 8 will be given an impulsein the direction of the sheave 9 and will consequently move slightly inthe direction of sheave 9 again and rotate in direction R (FIG. 3a).Such a rotation and translation of the transverse element 8 is necessaryfor positioning between both the sheave 9 and the sheave 10. Thetransverse elements 8 are generally also provided with a projection 12on one face and with a recess 12' on the opposite face, indicated hereby a dotted line. The projection/recesses 12, 12' of adjacent transverseelements thereby engage with each other and guide this translation androtation to some extent. For the rest, the projection/recess is notnecessary for the embodiment of the invention.

Through the translation and in particular the rotation, the transverseelement 8 will run out of true and will therefore also lie out of truebetween the sheaves 9, 10 of the pulley (FIG. 3b). The translation androtation are absolutely essential for taking the transverse elementsbetween the pulleys when the drive belt runs out of true, but inparticular from the point of view of slippage, wear and efficiency, itis undesirable for the transverse elements to be out of true in thepulley.

In U.S. Pat. No. 5,004,450 the flanks 13, 14 of the transverse element 8are shaped in such a way that the out-of-true position of the transverseelement 8 is corrected automatically during wedging in the pulleys.

However, the invention aims largely to overcome this out-of-trueposition already before wedging in the pulleys, in which case themeasures according to the US patent specification can also be-applied.

As shown in FIG. 3b, the transverse element 8 will rotate, but isslightly impeded therein by carrier 7a. The rotation of the transverseelement will therefore be about the first contact point 11 of carrier 7awith bearing surface 15 of the transverse element 8. On the other hand,the rotation is limited by a second contact point 16 of carrier 7b withtop surface 17 of the transverse element 8.

FIG. 4 shows the drive belt 6 according to the invention incross-section, with the transverse element 8 shown in the straightposition. The first contact point 11 of the bearing surface 15 withcarrier 7a in the case of tilting of the transverse element according toFIG. 3 and the second contact point 16 of the top surface 17 with thecarrier 7b in the case of tilting of the transverse element according toFIG. 3 are also shown here.

The first and second contact points 11, 16 respectively lie in the axialdirection of the drive belt 6 at a distance A. The carrier 7b and thesecond contact point 16 on the top surface 17 lie at a distance B.According to the invention, the drive belt must now be designed in sucha way that the arc tangent of the quotient B/A is smaller than 1°. Inthis way the transverse element, on the one hand, gains sufficientfreedom to translate and to rotate in order to position itself betweenthe pulleys, while, on the other hand, the tilting of the transverseelements is restricted already before the wedging in the pulleys, insuch a way that sufficient wedging of the transverse elements betweenthe pulleys is obtained, with improved efficiency of the transmission,reduced slippage and reduced wear. The drive belt is also relativelyeasy and cheap to manufacture.

In practice, it is found that in the range where the arc tangent liesbetween 0.2° and 0.8° in particular, the effectiveness is improved andthe efficiency increased. The arc tangent is preferably about 0.5°.

As can be seen in FIG. 2, it may be desirable for the transverseelements 8 on entering the pulley 3 to be capable of moving slightlyrelative to an adjacent transverse element in the axial direction 20 ofthe drive belt, in particular on contact with sheave 10. If transverseelements with projection/recess means 12, 12' are used, this movementcan be impeded. For that reason, the projection 12 of a transverseelement should preferably be accommodated with some play in the recess12'. Since in the main a relative movement of the adjacent transverseelements in the axial direction 20 can be desirable or necessary, it isgenerally sufficient to have play in essentially the axial directionbetween projection 12 and recess 12'. This is shown in slightlyexaggerated form in FIGS. 3a, 3b and 4, but it will be clear from FIG. 2that a play which permits a relative movement of adjacent transverseelements in the axial direction 20 corresponding to the projectedtangent in the axial direction 20 of the run-in hyperbola 21 of sheave10 at the position of the transverse element in question will suffice.

It will be clear that the invention is not limited to the embodimentsshown. For example, the invention can be applied in a corresponding wayto drive belts where one carrier or more than two carriers are beingused. The bearing surface and/or the top surface can also be profiled,e.g. convex, concave or slanting, possibly with an eccentric position ofthe top of the profiled surface. This profiling can be provided eitherin the lengthwise direction or in the transverse direction. Theprojection/recess means, if present, can also have differentconfigurations, such as cylindrical or conical.

I claim:
 1. A drive belt, comprising:an endless carrier means; a firstelement positioned transversely on said endless carrier means; saidfirst element being rotatable relative to said endless carrier means ina plane orthogonal to the longitudinal direction of said carrier means;said first element further comprising a bearing surface having a firstcontact point and a top surface having a second contact point, theshortest distance between said second contact point and said bearingsurface exceeding the thickness of said carrier means by a length B, andsaid first and second contact points disposed to engage opposite sidesof said carrier means when said first element rotates, thereby impedingexcessive rotation of said first element; said first and second contactpoints defining the hypotenuse of a right triangle having its rightangle vertex in the plane of said bearing surface, the distance betweensaid right angle vertex and said first contact point defining a lengthA; and the dimensions of said first element and said carrier means beingchosen such that the arctangent of the quotient B/A is greater thanabout 0.2 degrees but not greater than about 0.8 degrees.
 2. The drivebelt of claim 1 wherein the arctangent of the quotient B/A is equal toabout 0.5 degrees.
 3. The drive belt of claim 1 wherein said endlesscarrier means comprises first and second parallel endless carriers ofsubstantially equal thickness, and wherein said first contact point isdisposed to engage said first endless carrier and said second contactpoint is disposed to engage said second endless carrier.
 4. The drivebelt of claim 2 wherein said endless carrier means comprises first andsecond parallel endless carriers of substantially equal thickness, andwherein said first contact point is disposed to engage said firstendless carrier and said second contact point is disposed to engage saidsecond endless carrier.
 5. The drive belt of claim 1 wherein said firstelement further comprises a portion that extends outside the loopdefined by said endless carrier means, and wherein a first side of saidportion comprises a first projection extending in the longitudinaldirection of said carrier means, and wherein a second side of saidportion defines a recess for receiving a second projection provided by asecond element similar to said first element, and wherein the width ofsaid recess measured in the axial direction of the drive belt is largerthan the width of said first projection measured in the axial directionof the drive belt, such that said first and second elements may moverelative to one another in the axial direction of the drive belt, andwherein said first projection and said recess are both locatedsubstantially outside the loop defined by said endless carrier means. 6.The drive belt of claim 2 wherein said first element further comprises aportion that extends outside the loop defined by said endless carriermeans, and wherein a first side of said portion comprises a firstprojection extending in the longitudinal direction of said carriermeans, and wherein a second side of said portion defines a recess forreceiving a second projection provided by a second element similar tosaid first element, and wherein the width of said recess measured in theaxial direction of the drive belt is larger than the width of said firstprojection measured in the axial direction of the drive belt, such thatsaid first and second elements may move relative to one another in theaxial direction of the drive belt, and wherein said first projection andsaid recess are both located substantially outside the loop defined bysaid endless carrier means.
 7. The drive belt of claim 3 wherein saidfirst element further comprises a portion that extends outside the loopdefined by said endless carrier means, and wherein a first side of saidportion comprises a first projection extending in the longitudinaldirection of said carrier means, and wherein a second side of saidportion defines a recess for receiving a second projection provided by asecond element similar to said first element, and wherein the width ofsaid recess measured in the axial direction of the drive belt is largerthan the width of said first projection measured in the axial directionof the drive belt, such that said first and second elements may moverelative to one another in the axial direction of the drive belt, andwherein said first projection and said recess are both locatedsubstantially outside the loop defined by said endless carrier means. 8.The drive belt of claim 4 wherein said first element further comprises aportion that extends outside the loop defined by said endless carriermeans, and wherein a first side of said portion comprises a firstprojection extending in the longitudinal direction of said carriermeans, and wherein a second side of said portion defines a recess forreceiving a second projection provided by a second element similar tosaid first element, and wherein the width of said recess measured in theaxial direction of the drive belt is larger than the width of said firstprojection measured in the axial direction of the drive belt, such thatsaid first and second elements may move relative to one another in theaxial direction of the drive belt, and wherein said first projection andsaid recess are both located substantially outside the loop defined bysaid endless carrier means.